The present invention relates to a method and an apparatus for performing a fuel-air mixture for an internal combustion engine during a warmup phase.
To meet exhaust gas regulations for Otto engines, the operating states during the uncombusted hydrocarbons in the exhaust gas are due to so-called wall film effects, that is, to the deposition of fuel components from the fuel-air mixture on the cold engine walls in the intake tube and/or in the combustion chamber.
From German Patent Disclosure DE 195 22 075 A1, a method and an apparatus for forming a fuel-air mixture are already known in which during the cold-starting and warmup phase, fuel from a fuel tank is delivered to an evaporator, which functions in a relatively low temperature range from 60xc2x0 C. to 80xc2x0 C., since only relatively highly volatile components of the fuel (butanes, pentanes, hexanes) are intended to be used to form the fuel-air mixture. The fuel vapor created in the fuel evaporator is delivered via an adjusting device to an intake tube, downstream in the intake direction of a throttle valve, in order to obtain a fuel-air mixture in the intake tube.
Although with this known method a reduction in hydrocarbon emissions during the warmup phase can be achieved, nevertheless at the moment when fuel components come into contact with the cold aspirated air in the intake tube or as soon as they meet still-cold parts of the engine, they condense.
An internal combustion engine known from German Patent Disclosure DE 196 33 259 A1 has an evaporator, for fuel supply during the cold-starting and warmup phase, from which the fuel vapor is carried into a mixing chamber in which the fuel vapor is made turbulent with aspirated air to form a fuel-air mixture. The fuel-air mixture is delivered to an inlet region of the individual combustion chambers of the engine via a fuel separator, for separating individual relatively large droplets from the fuel-air mixture, which also includes high-boiling fuel components.
Once again, fuel condensation during cold starting and the warmup phase can only be reduced but not averted entirely, since despite the fuel separator, not all the high-boiling components can be removed from the fuel-air mixture.
From U.S. Pat. No. 4,323,046, an internal combustion engine is known that can be operated selectively with conventional fuels produced from petroleum or nonpetroleum fuels, especially alcohol. To that end, two fuel delivery systems are associated with the known internal combustion engine, and a switchover is made between them as needed.
The nonpetroleum fuel delivery system has an evaporator tank equipped with a heater, and from this tank a fuel-air mixture flows, regulated by a suitable gas pedal, directly into the intake elbow of the engine. For the cold-starting phase, the evaporator tank for the nonpetroleum fuels is equipped with a resistance heater, which is switched off when a certain temperature is reached.
The method according to the invention can be performed especially advantageously with a fuel delivery apparatus which has the advantage over the prior art that the cold-starting fuel used during the warmup phase comprises only low-boiling fuel components, and thus wall film effects in the intake tube and in the combustion chamber are virtually completely precluded, and hence the hydrocarbon emissions can be reduced sharply.
Since the low-boiling fuel components are recovered during the normal operation of the internal combustion engine, it is possible to perform a plurality of evaporation and condensation steps in succession, so that the low-boiling fuel components can be reliably separated out and enriched.
In the recovery of the cold-starting fuel during the normal operation of the engine, the engine running at its operating temperature can be used as a heat source for evaporating the low-boiling fuel components, and thus no additional heater is necessary.
In an advantageous feature of the invention, it is provided that to recover the low-boiling fuel components, the fuel that is to be delivered to the engine during normal operation is carried in liquid form through a first evaporation region of an evaporation and condensation system, and the fuel delivered to the evaporation and condensation system is preheated, while the fuel leaving the evaporation and condensation system in liquid form is cooled before being delivered to the engine.
In order to remove high-boiling fuel components from the cold-starting fuel to be recovered, the fuel evaporated in a first evaporation region of an evaporation and condensation system is subjected, beginning at a temperature of evaporation of approximately 60xc2x0 C. to 160xc2x0 C. in the first evaporation region, to a plurality of successive evaporation and condensation steps, until the temperature of evaporation in the region of a supply container serving to collect the cold-starting fuel has decreased to approximately 20xc2x0 C. to 40xc2x0 C.
In this way it becomes possible to create a cold-starting fuel which after an evaporation or atomization during the cold-starting and warmup phase, that is, while the engine is cold, condenses neither upon contact with the cold aspirated air nor upon striking cool engine walls.
In the fuel delivery from the separate supply container during the cold-starting and warmup phase, that is, in operation with the comparatively lower- boiling cold-starting fuel, additional provisions for fuel preparation and evaporation can effectively be employed.
In particular, it is possible that during the cold-starting and warmup phase, cold-starting fuel from the supply container is injected into an air intake line. If the injection takes place into an intake manifold, then along with the evaporation and condensation system and a heat exchanger, a single additional injection valve suffices for engine operation after the start.
Both in fuel injection and when fuel vapor is delivered, however, it can also be provided that during the cold-starting and warmup phase, the cold-starting fuel is introduced into the inlet region of each combustion chamber and metered individually for each combustion chamber.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawings.